High-speed wireline or fiber optic connections of backbone networks interconnecting nodes of a terrestrial radio access network are previously known. It is also known to interconnect radio base stations with microwave links providing interconnections of moderate data rates.
Increased antenna area of prior art microwave link antennas increases signal quality, but also increases irradiated microwave power as does transmission power increases. An increased antenna area can be achieved by arranging a plurality of smaller area antenna elements in an array.
Efficient modulations and signal constellations offer relieved power requirement, or improved performance if microwave power is maintained, as number of signal points in the signal constellation increases.
American Patent Application US2003/0125040 discloses a system for multiple-input multiple-output (MIMO) communication. A MIMO channel formed by NT transmit antennas and NR receive antennas is decomposed into Nc independent channels also referred to as spatial sub-channels, where Nc≦min{NT,NR}. Data is processed prior to transmission based on channel state information.
American Patent Application US2002/0039884 reveals a radio communication system with a transmitter having a plurality of transmitter antennas and a receiver having at least one antenna. Thereby a plurality of paths with various characteristics are formed between the transmitter antennas and the at least one receiver antenna. Data is assigned one or more categories. Depending on categories and path characteristics, the data is mapped to one or more of the transmitter's parts and antennas.
American Patent Application US2002/0039884 describes a radio communication system with a transmitter having a plurality of transmitter antennas and a receiver having at least one antenna. Data tags indicate data importance or other requirements. Data is assigned one or more categories. Depending on categories and path characteristics, the data is mapped to one or more of the transmitter's parts and antennas.
3rd Generation Partnership Project (3GPP): Technical Specification Group Radio Access Network, Physical layer aspects of UTRA High Speed Downlink Packet Access (Release 4), 3G TS 25.848 v 4.0.0, France, March 2001, describes MIMO open loop signal processing of MIMO transmitter and receiver in section 6.5.
Bell Labs Technical Journal, autumn 1996: G. Foschini, “Layered Space-Time Architecture for Wireless Communication in a Fading Environment When Using Multi-Element Antennas” shows that under fading conditions with statistically uncorrelated identically distributed propagation channels, the bandwidth constrained channel capacity of a MIMO channel, CMIMO, scales on average asCSISO·min{M,N},  (1)where CSISO is channel capacity of a SISO channel, and M and N are number of antenna elements at receiver and transmitter side, respectively. For a band limited (bandwidth B) AWGN (Additive White Gaussian Noise) channel the SISO channel capacity equalsCSISO=B·log2(1+SNRSISO) [bits/s],  (2)where SNRSISO is the SISO channel signal to noise ratio.
FIG. 1 schematically illustrates N transmitter antenna elements <<T1, T2, . . . , TN>> and M receiver antenna elements <<R1, R2, . . . , RM>> in MIMO communications. Between the various transmitter and receiver antenna elements there are propagation channels <<h11, h12, . . . h1M, . . . , hNM>>.
The individual propagation channels, that are SISO (Single Input Single Output) channels, form a MIMO channel.
C. Schlegel and Z. Bagley, “Efficient Processing for High-Capacity MIMO Channels” submitted to JSAC, MIMO Systems Special Issue: Apr. 23, 2002 reveals estimation of optimum channel capacity of a MIMO system for a known MIMO-channel described by channel matrix H by means of singular value decomposition, SVD.U·S·VH=SVD{H},  (3)where U and V are unitary matrices, S is a resulting diagonal matrix with singular values in the main diagonal, and VH is a Hermitian transformed matrix V.
A. Goldsmith, S. A. Jafar, N. Jindal, S. Vishwanath, “Capacity Limits of MIMO Channels” IEEE Journal on Sel. Areas in Comm., Vol. 21, No. 5, June 2003 provides results on capacity gain obtained from multiple antennas in relation to channel information at receiver or transmitter, channel signal-to-noise ratio, and correlation between channel gains of each antenna element. The paper also summarizes results for MIMO broadcast channel, BC, and multiple access channel, MAC, and discusses capacity results for multicell MIMO channels with base station cooperation, the base stations acting as a spatially diverse antenna array.
In accordance with Goldsmith et al., the MIMO channel capacity for flat fading channel conditions, in the case of equal number of antenna elements for transmitter and receiver antennas, is
                                                                                          C                  MIMO                                =                                                      B                    ·                                          log                      2                                                        ⁢                                                                          ⁢                                      (                                          det                      ⁢                                                                                          ⁢                                              {                                                  I                          +                                                                                    SNR                              N                                                        ⁢                                                          H                              ·                                                              H                                H                                                                                                                                    }                                                              )                                                                                                      [                                  bits                  /                  s                                ]                                                    ,                            (        4        )            assuming uncorrelated channels of the various sending antenna elements.
P. Kyritsi, “MIMO capacity in free space and above perfect ground: Theory and experimental results” 13th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications 2002, vol. 1, pp. 182-186, September 2002 studies the capacity potential for propagation in free space over perfect ground. Theoretical predictions are compared with measurements over an empty parking lot with nearly flat surface.
None of the cited documents above discloses particular antenna configurations related to communications distance with line of sight, LOS, MIMO communications.